6H-SiC pn结紫外光探测器的模拟与分析

运用器件模拟软件模拟了pn结6H-SiC紫外光探测器的光响应灵敏度特性.讨论了不同掺杂浓度、不同器件结深对响应灵敏度的影响.对于p+n结器件，当受光面为p+层，且厚度约为0.2μm、浓度约为9×10.18cm-3、n层浓度约为1×1 0.16cm-3时，器件有较大的响应灵敏度，R=167.2mA/W；当受光面为n+ 层 ，且厚度约为0.2μm、浓度约为9×10.18cm-3、p层浓度约为1×10.16cm-3时，器件有较大的响应灵敏度，R=183.5mA/W.通过比较可知，模型能较好地反应实际情况，与实验数据符合较好. 关键词： 6H-SiC 紫外光探测 吸收系数 光响应灵敏度     

Binary response Se/ZnO p‐n heterojunction UV photodetector with high on/off ratio and fast speed

A high‐performance UV photodetector (PD) based on a p‐Se/n‐ZnO hybrid structure with large area (more than 1×1 cm) is presented in this study. The device is theoretically equivalent to a parallel‐connection circuit for its special structure and shows multifunction at different voltage bias, which means the output signal can be tailored by an applied voltage. The Se/ZnO PD shows binary response (positive and negative current output under on/off periodical light illumination) under small reverse bias (–0.05 V and –0.1 V) which efficiently reduces the negative effect of noise signal in weak‐signal detection applications. At zero bias, with the aid of a p‐n heterojunction, a high on/off ratio of nearly 10⁴ is achieved by this device at zero set bias under 370 nm (∼0.85 mW cm⁻²) illumination and this on/off ratio can be achieved in 0.5 s. The device also shows a fast speed with rise time of 0.69 ms and decay time of 13.5 ms measured by a pulse laser, much faster than that of a pure ZnO film. The Se/ZnO PD in this research provides a new pathway to fabricate multifunctional high‐speed, high signal‐to‐noise ratio, high detectivity and high selectivity UV photodetectors.

     

Significant photoelectrical response of epitaxial graphene grown on Si-terminated 6H-SiC

Photoelectrical response characteristics of epitaxial graphene (EG) films on Si- and C-terminated 6H-SiC, and transferred chemical vapor deposition (CVD) graphene films on Si-terminated 6H-SiC have been investigated. The results show that upon illumination by a xenon lamp, the photocurrent of EG grown on Si-terminated SiC significantly increases by 147.6%, while the photocurrents of EG grown on C-terminated SiC, and transferred CVD graphene on Si-terminated SiC slightly decrease by 0.5% and 2.7%, respectively. The interfacial buffer layer between EG and Si-terminated 6H-SiC is responsible for the significant photoelectrical response of EG. Its strong photoelectrical response makes it promising for optoelectronic applications.     

二维6H-SiC光学特性的应变调控

为了减小6H-SiC的带隙、提高对可见光的吸收效率和载流子迁移速率,采用第一性原理研究了应变对6H-SiC的能带结构、光学吸收系数、载流子迁移率以及光催化特性的影响。结果表明：应变能够降低6H-SiC的导带底,但对价带顶没有影响,导致带隙减小。随着应变的增加,吸收曲线向低能级方向移动,即发生红移,有利于可见光的吸收。施加应变后空穴的载流子迁移率提高,有利于载流子移动,且空穴的载流子迁移率是电子的2.5倍,有利于空穴和电子的分离。综合应变对带隙大小、带边位置的影响可知,应变在±2%、±4%时对可见光的吸收以及光催化制氢最有效。综上所述,应变能够对6H-SiC的光学吸收和光催化特性有很好的调控作用。     

桑叶的红外光谱和紫外光谱研究

桑叶为药食两用的原料,具有降血糖、降血压、降血脂、延缓衰老等多种保健功效。本文首先采用了傅立叶变换红外光谱法直接、快速、准确地测定了桑叶的红外光谱图,根据桑叶的峰位,我们可以推断出桑叶可能含有醇、酚、烷烃、烯、蛋白质和多糖等化学成分;然后进行了紫外光谱分析及红外光谱和紫外光谱的对比分析,其结论为桑叶的识别、鉴定和药理分析提供了一定的科学依据。     

紫外辐射照度计的余弦响应特性测试研究

采用所研制的紫外辐射照度计余弦响应特性测试平台,对21种市面上常用的商业紫外辐射照度计进行了余弦响应特性测试。测试结果表明,不同型号、不同探测器结构、不同漫射器材料的紫外辐射照度计的余弦响应特性差异较大,客观地反映了当前紫外辐射照度计的水平。当入射角为±10°时,余弦误差变化范围为0.03%～15.83%;当入射角为±30°时,余弦误差变化范围为1.85%～73.66%;当入射角为±60°时,余弦误差变化范围为1.82%～65.04%。在实际测量中,经常会用到大面积的紫外辐射光源或是形状不规则如长条形的紫外辐射光源,在测试时不能保证光线垂直入射到探测器,同时也不能满足点光近似条件,测试结果误差较大。通过测试可以准确地了解当前紫外辐射照度计的余弦响应特性,用于指导实际的实验测试,合理地调整测试条件以满足测试需求,必要时可进行相应的余弦误差修正。     

The effect of UV irradiation on temperature dependence of photoluminescence and photoacoustic response in porous silicon

The influence of UV irradiation on temperature dependence of the integral intensity of luminescence I _lum(T) in porous silicon was studied. It was found that, if luminescence decays with temperature nonmonotonically, the peak of I _lum(T) shifts toward higher temperatures as the exciting radiation density increases. Under UV irradiation, the function I _lum(T) becomes monotonically decreasing. If the function I _lum(T) is initially monotonically decreasing, UV preirradiation changes the emission spectrum and accelerates temperature quenching of the red-orange emission band. The variation of the amplitude of the pulsed photoacoustic response with UV irradiation dose was studied. The dependence found is explained by the removal of foreign inclusions from the developed surface of porous silicon. An energy level diagram that makes it possible to explain the behavior of I _lum(T) is suggested. It is noted that the shape of the function I _lum(T) can be used as a test whereby the contributions from dissimilar oscillators to the red-orange emission band are estimated.     

Sn-C60薄膜的紫外吸收光谱和X-射线衍射谱分析

对Sn-C60薄膜进行紫外可见光吸收，X-射线衍射和扫描电镜的测定结果显示，薄膜样品紫外可见光吸收的两个短波段吸收峰比纯C60薄膜的吸收峰显著下降，说明Sn-C60薄膜的电子光吸收跃迁为间接跃迁，能带中有杂质能级的存在；样品的X射线衍射峰则对应于面心立方结构；扫描电镜结果显示薄膜为纳米级颗粒组成。     

Doping and temperature dependence of electronic Raman response in cuprate superconductors

The doping and temperature dependence of the electronic Raman response in cuprate superconductors is studied within the kinetic energy driven superconducting mechanism. It is shown that the temperature dependent depletion at low-energy shifts is faster in the B1g symmetry than in the B2g symmetry. In analogy to the domelike shape of the doping dependent superconducting transition temperature, the maximal peak energy in the B2g channel occurs around the optimal doping, and then decreases in both underdoped and overdoped regimes. Moreover, the overall density of Cooper pairs increases with increasing doping in the underdoped regime.     

Theoretical analysis of the effect of temperature dependence of Auger coefficient on the turn-on time delay of uncooled semiconductor laser diodes

In this paper, a novel interpretation of the effect of Auger recombination coefficient (C) on the turn-on time delay (t_on) of semiconductor laser diodes (SLDs) is presented. To the date, the well-known conclusion is that the main effect of C is to decrease t_on. This is because the earlier studies were based on less physical assumptions. Contrarily, we show that the general effect of C is to increase t_on. This conclusion is supported by including the effect of temperature of operation (T) on t_on of uncooled SLDs. Advanced analytical model is presented to determine t_on analytically and in term of nonradiative (A), radiative (B) and C recombination coefficients. The derived model can be applied to bulk and multiple quantum-well (MQW) long-wavelength SLDs at any value of temperature of operation degree (T) within the range 25-85 °C. The temperature dependence of t_on is calculated according to the temperature dependences of C and threshold carrier density (N_th). The temperature dependence of the latter is calculated according to the temperature dependence of laser cavity parameters and not by the well-known Parkovian relationship. Numerical and analytical results show that t_on increases as T increases due to increasing of N_th and C which its effect dominates at high temperature degrees. In addition, we show that the effect of temperature dependence of t_on in MQW SLD is smaller than the bulk one. Moreover, MQW SLD needs a lower injection current than the bulk one to achieve the same value of t_on.     

紫外光谱法检测COD中硝酸盐与温度影响的研究

以邻苯二甲酸氢钾配制的化学需氧量标准液为实验对象,采集1~800mg·L-1标准液的紫外吸收光谱,运用偏最小二乘法(PLS)建立了不同谱区的校正模型,结果表明,265~310nm谱区模型的相关性最高,误差最小;为了消除硝酸盐与温度对化学需氧量测量的影响,分别研究了不同浓度的硝酸钠与不同温度条件下标准液的紫外吸收光谱的变化情况,结果表明硝酸钠在208~238nm有明显的吸收,265~310nm谱区模型不受硝酸钠吸收的影响,温度的升高会导致标准液的紫外光谱吸光度的增大,通过预测分析建立了不同校正模型下的温度补偿函数。     

三嵌段共聚物SEBS中自由体积行为的温度及e+辐照时间依赖性的研究

利用正电子湮没寿命谱实验手段研究了²²Na放射源的e⁺自辐射对三 嵌段共聚物SEBS的正电子湮没参数的影响，而后结合Eldrup的经典模型，研究了SEBS的自由体积孔尺寸和自由体积分数随着温度的变化关系，给出了自由体积分数在T_g以上和在Tg以下各自区域内分别与温度呈线性关系，最后结合Williams-Landel-Ferry(WLF)自由体积理论和Eldrup的经典模型讨论了热膨胀系数和自由体积分数中的A常数. 关键词： 正电子湮没技术 嵌段共聚物 自辐射 热膨胀     

石墨烯低温热膨胀和声子弛豫时间随温度的变化规律

考虑到原子非简谐振动和电子-声子相互作用,用固体物理理论和方法研究了石墨烯格林艾森参量和低温热膨胀系数以及声子弛豫时间随温度的变化规律,探讨了原子非简谐振动项对它们的影响.结果表明:1)在低于室温的温度范围内,石墨烯的热膨胀系数为负值,随着温度的升高,其热膨胀系数的绝对值单调增加,室温热膨胀系数为-3.64×10~(-6)K~(-1);2)简谐近似下的格林艾森参量为零.考虑到非简谐项后,格林艾森参量在1.40-1.42之间并随温度升高而缓慢增大,几乎成线性关系,第二非简谐项对格林艾森参量的影响小于第一非简谐项;3)石墨烯声子弛豫时间随着温度的升高而减小,其中,温度很低(T10 K)时变化很快,此后变化很慢,当温度不太低(T300 K)时,声子弛豫时间与温度几乎成反比关系.     

密度泛函理论方法研究6H-SiC(0001)表面对氧分子和水分子的吸附

本文通过密度泛函方法计算6H-SiC(0001)表面对氧分子和水分子的吸附. 在6H-SiC(0001)表面上吸附的O₂分子自发地解离成O^*,并被吸收在C与Si原子之间的空位上. 吸附的H₂O自发地分解成OH^*和H^*,它们都被吸附在Si原子的顶部,OH^*进一步可逆地转化为O^*和H^*. H^*可以使Si悬键饱和并改变O^*的吸附类型,并进一步稳定6H-SiC(0001)表面并防止其转变为SiO₂.     

Comparison of the Morphological,Mechanical, and UV Protection Properties of TiO2/Polyamide 6 (PA6), and ZnO/PA6 Nanocomposite Multifilament Yarns

The properties of TiO₂/polyamide 6 (PA6) and ZnO/PA6 nanocomposite filament yarns produced on a pilot-plant melt spinning machine were compared. Concentrated masterbatches were prepared using a twin screw extruder. Then continuous multifilament yarns were produced by blending nylon 6 chips and various amounts of the prepared masterbatches. Melt spinning was carried out at the spinning temperature of 265°C and take-up speed of 4000 m/min. As-spun multifilament yarns were then drawn and textured. Morphological properties of the produced yarns were studied. Thermal behavior and physical properties, including shrinkage and tensile properties, were measured. Weft-knitted fabrics were evaluated for their ultraviolet protection properties. Although both kinds of the nanoparticles had a positive effect on the ultraviolet protection properties of their nanocomposite fabrics as compared to pure PA6 fabric, the efficiency of the TiO₂ nanoparticles was more than that of the ZnO ones for the same concentrations. The differences between the different properties of the two kinds of nanocomposites are discussed based on their interaction with the polymeric matrix, specific surface area, steric hindrance effect, and band gap energies.     

Experimental (UV,NMR, IR and Raman) and theoretical spectroscopic properties of 2-chloro-6-methylaniline

In this work, the experimental and theoretical UV, NMR and vibrational spectra of 2-chloro-6-methylaniline (2-Cl-6-MA, C₇H₈NCl) were studied. The ultraviolet absorption spectra of compound that dissolved in ethanol were examined in the range of 200–400 nm. The ¹H, ¹³C and DEPT NMR spectra of the compound were recorded. FT-IR and FT-Raman spectra of 2-Cl-6-MA in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies were found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the calculated NMR chemical shifts and absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Computer programs for processing of UV and visible absorption spectra

A mathematical method for calculation of the stability constants of complexes by spectrophotometric data is represented. The program algorithm SQCONS is developed based on the method of nonlinear squares. As a test example, a calculation of the constant and the molar coefficients of extinction of the monosulfate complex CuSO ₄ ⁰ is presented. Institute of Mineralogy and Petrography of the Siberian Division of the Russian Academy of Sciences, 3, Universitetskii Ave., Novosibirsk, 630090, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 4, pp. 581–586, July–August, 1998.     

Nonlinearity in Intensity versus Concentration Dependence for the Deep UV Resonance Raman Spectra of Toluene and Heptane

Abstract: The relation between Raman scattering, resonance Raman scattering, and absorption is reviewed to determine to what extent quantitative analysis can be applied in resonance Raman spectroscopy. In addition, it is demonstrated experimentally that normal Raman spectra can be dramatically inhibited by absorption and resonance Raman effects. Raman spectra of toluene and heptane mixtures—with progressively increasing concentrations of heptane—were measured using 229-nm laser excitation. The results show that the characteristic band intensities are not directly proportional to the relative concentrations of the compounds and deviate due to absorption resonance effects. An approximated mathematical model is developed to demonstrate that the intensities of the normal Raman scattering bands are suppressed. An inhibition coefficient K_i is introduced to describe the situation and determine the penetration depth. Most remarkably, it is shown that the intensity of the resonance Raman scattering bands can be constant even when the concentration ratios differ substantially in the sampled mixtures.     

非高斯噪声激励下含周期信号FitzHugh-Nagumo系统的响应特征

研究了非高斯噪声激励下含周期信号的FHN模型的动力学行为. 通过计算神经元的平均响应时间、观察神经元的共振活化和噪声增强稳定现象,分析了非高斯噪声对神经元动力学行为的影响. 发现通过改变非高斯噪声的相关时间可以有效地改变共振活化和噪声增强稳定现象. 观察到在强相关噪声下不同强度的非高斯噪声抑制了神经元的噪声增强稳定现象而共振活化现象几乎不变,也就是非高斯噪声有效地增强了神经响应的效率. 观察了平均响应时间与非高斯噪声参数q之间的关系,当q为一个有限的小于1的值时,平均响应时间取得最小值. 最后表明在一定条件下,非高斯噪声出现重尺度现象,即非高斯噪声产生的效果可以由高斯白噪声来估计. 关键词： FHN神经系统 非高斯噪声 平均响应时间 共振活化现象